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A s y m m e t r i c A d d i t i o n R e a c t i o n s i n t h e P r e s e n c e o f [ 2 . 2 ] P a r a c y c l o p h a n e L i g a n d s Abstract: Planar and central chiral [2.2]paracyclophane ligands have been designed and used in the highly enantioselective addition of alkyl, alkenyl, alkynyl and aryl zinc reagents to aldehydes and imines.

Dedicated to Professor Dieter Seebach for his achievements in asymmetric catalysis.Abstract: The synthesis of enantiomerically pure compounds is one of the major challenges in organic synthesis. In this review, we present the state of the art in asymmetric catalysis using immobilized chiral ligands and complexes for asymmetric C À C and Cheteroatom bond forming reactions. Chiral catalysts based on dendrimers and soluble polymeric supports are considered. In particular, addition reactions to carbon-carbon double bonds, asymmetric 1,2-addition reactions using, e.g., dialkylzinc reagents, metalcatalyzed substitution reactions and cycloaddition reactions are covered. Specific emphasis is placed on enantioselective epoxidation and aldol reactions. A further aspect is the (hetero) Diels±Alder reaction catalyzed by immobilized ligands.

We present herein the first indications for dimeric structures in cometal-free asymmetric conjugate addition reactions of dialkylzinc reagents with aldehydes. These are revealed by nonlinear effect (NLE) studies. A monomer-dimer equilibrium can be assumed which explains the increase of the ee value in the product over time. Also, DOSY NMR spectroscopic measurements indicate the existence of the catalyst as [LZnEt](n) complexes in solution. Additionally, the first X-ray structure of a zinc complex with a [2.2]paracyclophane ligand was determined. The structures of the zinc complexes are supported by DFT calculations of monomeric and dimeric species.

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